docs: def json(self, branch='master', filename=''):
          """Retrieve _filename_ from GitLab.
  
          Args:
              branch (str): Git Branch to find file.
              filename (str): Name of file to retrieve.
  
          Returns:
              dict: Decoded JSON.
  
          Raises:
              SystemExit: Invalid JSON provided.
  
          """
          file_contents = self.get(branch=branch, filename=filename)
  
          try:
              json_dict = json.loads(file_contents)
          # TODO: Use json.JSONDecodeError when Python 3.4 has been deprecated
          except ValueError as error:
              msg = ('"{filename}" appears to be invalid json. '
                     'Please validate it with http://jsonlint.com. '
                     'JSON decoder error:\n'
                     '{error}').format(
                         filename=filename, error=error)
              raise SystemExit(msg)
  
          LOG.debug('JSON object:\n%s', json_dict)
          return json_dict